Last week’s spill damaged this portion of the Eastern Promenade Trail and sent about 1.69 million gallons of partially treated wastewater into Casco Bay. Staff photo by Gregory Rec A report prepared by the Portland Water District says human error caused a large wastewater spill from its treatment plant that washed away part of the Eastern Promenade Trail last Thursday morning and flowed into Casco Bay. The report also says more than 1.5 million gallons of wastewater spilled, not the estimated 1 million gallons reported initially. Jessica Grondin, spokeswoman for the city of Portland, said the trail would reopen Wednesday. “East End Trail is on schedule to be reopened tomorrow, most likely midday,” Grondin tweeted Tuesday.